1. Field of the Invention
The present invention relates to video signal processing circuits in NTSC and PAL systems and in a high definition television (hereinafter referred to as “HDTV”) system, viewfinder apparatuses including the video signal processing circuits, television cameras including the viewfinder apparatuses, and image monitor apparatuses including the video signal processing circuits.
2. Description of the Related Art
Hitherto, video signal contour-adjusting circuits have been employed to improve the resolution of an image in a viewfinder apparatus for a television camera by enhancing the contour of the image to be captured and therefore to enable a user to easily observe the image.
In general, the video signal contour-adjusting circuits separate a part of the video signal where the temporal variation is great, which in turn is amplified and added to the original signal.
To this end, a method described below has been widely used. Specifically, low-pass filters, each of which includes an inductor as a serial device and a capacitor as a parallel device of an input signal, are connected in multiple stages to generate a delayed signal of the original signal. The delayed signal is added to the original signal, and the contour is thereby emphasized.
Since the low-pass filters formed of the inductors and the capacitors are connected in multiple stages in the above method, a plurality of inductors and capacitors are required. These components are difficult to be miniaturized. When these components are mounted in a small apparatus, they are apt to pick up electromagnetic noise generated by peripheral devices. Therefore, it is necessary to construct an electromagnetic shielding. Hence, the cost of such an apparatus is high.
If an amplification degree is increased so as to strongly perform contour adjustment by the contour-adjusting circuit, a circuit is more apt to oscillate and an operation of the apparatus becomes unstable.
If the apparatus is a television camera both in an NTSC/PAL system and an HDTV system, it is necessary to arrange a plurality of contour-enhancing circuits since frequency bands of the video signals and signal processing methods differ according to the systems. It is thus difficult for the television camera to be miniaturized and low-cost.